Thickened aqueous ammonium nitratehexamethylenetetramine explosive containing ammonium perchlorate as sensitivity stabilizer



United States atent 3,409,486 THICKENED AQUEOUS AMMONIUM NITRATE- HEXAMETHYLENETETRAMINE EXPLOSIVE CONTAINING AMMONIUM PERCHLORATE AS SENSITIVITY STABILIZER Dale S. Partridge, Shawnee Mission, Kans., assignor to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed Dec. 20, 1967, Ser. No. 691,949 3 Claims. (Cl. 14921) ABSTRACT OF THE DISCLOSURE In thickened aqueous suspension explosives based principally on ammonium nitrate in combination with a suspended solid fuel, sensitized and stabilized with dissolved hexamethylenetetramine, variation of sensitivity with changing temperature is suppressed by incorporation of about 2 weight percent ammonium perchlorate in the composition. Charges of explosive thickened with hydroxy-substituted thickening agents are conveniently pumped into place Without viscosity problems at low temperatures by injection of the gelling agent (borax) into the pump exit stream.

SUMMARY OF THE INVENTION There has recently come into use in quarrying and mining a class of explosives which are essentially thickened aqueous suspensions containing both solid and dissolved ammonium nitrate in combination with suspended solid fuel. These compositions are sensitized with various substances and must be stabilized to prevent gas generation or deterioration during storage. It has been discovered that a class of aqueous suspension explosives can be both sensitized and stabilized against deterioration in storage by incorporation of a minor amount of hexamethylenetetramine in the compositions. However, the sensitivity of this class of formulations has been found to decline in cold weather, so that larger quantities of high explosive are required in the booster charge in order to initiate the explosion of the main charge. The combined effects of less sensitivity and increase of viscosity at low temperatures often render a batch of explosives unsuitable for low temperature use. In a typical example, a formulation which was found to have a critical diameter of five inches for detonation could be initiated with a booster charge of only 20 grams of pentolite at 90 F. but at 45 F. a one-pound pentolite booster was required. Between one and two weight percent ammonium perchlorate was added to a formulation of this type without any apparent effect at 90 F. However, it has been found that the sensitivity of the resulting composition is almost the same at 45 F. as it is at 90 F.

This improvement with respect to variation of sensitivity with temperature is obtained by inclusion of at least one Weight percent ammonium perchlorate in compositions comprising at least 15 weight percent water, at least 40 weight percent ammonium nitrate, at least 0.5 weight percent finely divided solid fuel, at least 1.0 weight percent dissolved hexamethylenetetramine, sufficient to improve sensitivity, and a minor amount of water-dispersible thickening agent.

Preferred stable, thickened aqueous dispersion explosive compositions comprise (a) about to 30 weight percent water,

(b) about 40 to 80 Weight percent ammonium nitrate (c) about 5 to weight percent sodium nitrate (d) about 3 to 10 weight percent hexamethylene tetramine 3,409,486 Patented Nov. 5, 1968 (e) from zero to 5 weight percent aluminum powder of less than 50 mesh size (US. Standard Series) (f) from 3 to 15 weight percent granular aluminum (g) about 2 weight percent ammonium perchlorate, sufficient to stabilize the composition against variation of sensitivity with changing temperature; and

(h) sufiicient water-soluble thickening agent to stabilize the composition against settling of solids.

DETAILED DESCRIPTION OF THE INVENTION As indicated above, considerable variation is possible in the formulation of the preferred explosive compositions. Such flexibility in formulating is desirable in order to be able to fit the explosive to the requirements of the situation, that is, diameter of the shot hole, hardness, density and integrity of the material which is being blasted and the distance from the face of the deposit at which it is intended to load the dislodged material. Brisance, heaving ability and total power should all be capable of some adjustment. Fortunately this can be done within the limits disclosed above without sacrificing the substantial immunity to eflfects of ambient temperature on sensitivity. The following discussion and specific example serve to explain and illustrate the practice of the invention.

A slurry blasting composition was prepared by mixing the ingredients listed below in the parts by weight as indicated.

Ingredients: Parts by weight Ammonium nitrate prills 46.2 Granular aluminum (94 to 100% passes No. 8

US. Series sieve, maximum of 5% passes 100- mesh U.S. Series) 15.0 Sodium nitrate 10.0 Hexamethylenetetramine 3.0 Aluminum powder (paint grade flake) 1.0 Guar gum 0.8 Water 24.0

To illustrate the variation of sensitivity with temperature, tests were made at various temperatures as indicated below:

Temperature Critical Diameter Primer Required 5 1 1b. Pentolite. 5 g. Pentolite. 5 20 g. Pentolite.

Example The slurry explosive prepared as described .above was mixed with 2 percent ammonium perchlorate and separate charges were tested at both high and low temperatures. Results are tabulated below.

Percentage Temperature, 11. Critical Diameter, j Ammonium Perchlorate inches Batch No. Age Temperature, F. Critical Diameter,

inches ,67 3 65 3 40 33 2 days 3% Both batches showed no apparent variation of critical charge diameter after storage for 30 days.

In placing charges of slurry explosives at low temperatures another problem arises as a result of high viscosity of the mixture. Normally slurry explosives contain both. a water-soluble thickening agent and a cross-linking or gelling agent, so that the resulting product is a stable suspension of solids in a pumpable gel. At low ternperaev tures, however, this type of product is difficult to pump and must be packaged for handling.

I have found, that a stable charge can be placed in'a hole, even in below-freezing weather by pumping the aqueous suspension explosive compositions of this invention into place with a tube-squeezing pump of the type used to pump concrete and grout and injecting the gelling agent into the exit stream from the pump so that as the material exits from the end of the hose it is in a crosslinked (i.e. water resistant) state. In this Way, the pump ing of viscous gels is avoided and yet the suspension is stabilized in place immediately when the material is placed in the hole. Preferred thickening agents are hydroxy-substituted thickeners, including polysaccharide gums, soluble modified starches and hydroxy-substituted polymers such as polyvinyl alcohol. The preferred gelling agent is borax, preferably in the form of saturated aqueous solution. The type ofipump. used to handle theslurry may be,,tor examp1e,.one..of..the sort described in-U SrPate'nt 9. 3 2- ..I claim;

:LJnan aqueous su pensionexplosive-compqsitioncorm prising atleast 15 .weight percentwater, at least 40 weight percentammonium nitrate, at least,0.5..weight percent finely divided solid fuel, at',l ea st ,1-,O-,weightpercent; dis.- solved,hexamethylenetetramine, suflicient ,to improve-sensitivity and a minoramountof water-.dispersible.thickening. agent the improvement,c;onsisting of incorporating in the composition at least one. weight percent ammonium perchlorate-,suffiqient to' reduce the variation of sensitivity ofl-the compgsitiomresulting from change= of;=ternperaturex .Z.. Avstable, thickened aqueous suspension: xplosiye composition comprising w (a) .aboutlO-to 30 weight percent waten,--. 5r nib) gabout 40 to-80 weight percent ammoniummitrate', -(c). about 5 to 15v Weight percent sodium nitrate,

,(d) about 3,;to- 10-weight percent hexamethylenetetra l"ml1'1e, H" 7 "1 a e'-) from-zero to .5? weight percent aluminum .powder of less than.50.mesh size (US. Standard Series),; (f) from 3 to 15 Weight percent granularaluminumy .(g).;about. '2. weight percent, ammonium 1' perchlorate -suflicient.-;to stabilize the composition against'variation of sensitivity with changing temperature; and '-(h) sufficient water-solublethickening .agent to stabilize thea composition against settling of-solids. 3. Forming in place; a stable,- gelled suspension explosi-ve' composition bypumping into a-hole an aqueous slurry;comprising-,:.-

.-(a)1at least; 15 weight percent water,. .--t(b) atleastz40 weight percent-ammonium nitrate, .-(c) atleast 0.5 weight -percent-finely divided solid fuel, "(d) atleast lweight percent dissolved hexamethylenee tetramine sufficient to improve sensitivity,

(e) at least 1 Weight percent ammonium perchlorate,

. --suflicient to. :stabilize the composition againstvariation of sens-itivity with changing temperature; and .-:('f)-'a. stabilizing amount of. a water-soluble hydroxyw?- substituted thickening agent and injecting into the exit stream: from the'pump sufiicient borax topro- -duce an-im'mediate gelling-effect.

ReferencesjCited UNITED STATES PATENTS 3,166, 13; 11/,1965, Gordon Q I 149'- 46 3,156,555. 11/1965. Gordon ,149-4 3,247,033" 4/1966 Gordon 1149-1s 3,299,691 12/19, 66, .Gordon 149 n1; QL IARFORTILP rimaIy g mm 1. LECHERT, JR., Assistant Examiner. 

